1. Technical Field
The invention relates generally to etching methods, and more particularly, to methods for opening a hard mask and a silicon-on-insulator (SOI) substrate in a single process chamber.
2. Background Art
Silicon-on-insulator (SOI) substrates are increasingly used with trenches for structures, such as trench capacitors, to provide further improvement of semiconductor device performance. However, forming trenches in an SOI substrate presents a number of challenges. For example, SOI substrate trenches require etching multiple layers including a silicon dioxide (SiO2) based hard mask, a silicon nitride (Si3N4) pad layer, a silicon dioxide (SiO2) pad layer, and the silicon-on-insulator (SOI) layer and a buried silicon dioxide (SiO2) (BOX) layer of the SOI substrate. Because each etch chamber is conventionally designed and optimized to etch a specific material, etching multiple layers usually requires multiple etch process steps performed in multiple chambers in order to achieve a desired trench profile. For example, etching the SOI substrate requires use of another process chamber. Transferring wafers from one chamber to another increases the time required to complete the process. In addition, multiple chambers increase equipment expense. The above-described processes also may result in non-uniform SOI openings across an entire wafer, consumption of photoresist prior to etching of the BOX layer, and inadequate profile control. There is therefore a need in the art for a solution to the problems of the related art.